Mystified by all the caterpiller talk at WSO? No worries! The College is not afraid to act.

To the Williams Community,

People have asked about the sudden appearance of, shall we say, rather a few caterpillars on campus and in other parts of town and what’s being done about it.

No, we’re not living in a Hitchcock movie. They’re called forest tent caterpillars, because of the tent-shaped nests they build in trees. They were here last year, too, and are capable of eating almost all the leaves on a tree.

To prevent this, grounds staff is applying to affected trees a bacterium called Bacillus thuringiensis (Bt).

Bt is the only microbial insecticide on the market that is a naturally occurring bacterium. It is commonly found in soils throughout the world. Bt produces proteins that shut down the caterpillars’ digestive systems in a couple days. It’s considered non-toxic to people and to all non-target species. Its use is even recommended for food crops.

The current infestation is significantly worse than in prior years. The populations are so high that the caterpillars are moving from tree to tree via silken webs, looking for additional food sources and are feeding on plant material not normally attacked. For this reason it’s very difficult to establish a precise spray schedule, so spray sites are determined almost daily as the caterpillars arise and new foliage emerges.

We anticipate applying Bt for the next 2-3 weeks during the caterpillars’ most vulnerable stage. It’s impractical to spray every tree on campus so we’re concentrating on the most significant ones. We’re also sensitive to people and property and so are making every effort to minimize the impact on both. Trees that have been sprayed will be posted for 24 hours with a yellow caution sign.

Please call me at x3304 with any questions. Or contact our Service Desk at x2486 to notify us of an outbreak in your area of campus.

Meanwhile, we also recommend you keep your car windows closed since some people have returned to their cars only to find a large furry wriggling surprise.

Eventually they’ll turn into moths, which will prove a boon to the local bat
population. But that’s a story for another time.

Dave Fitzgerald
Horticulturist and Grounds Supervisor

“Considered non-toxic” by whom, I wonder. Are naturally occuring pesticides regulated by the FDA and/or OSHA? I suspect not.

With luck, Diana will post some photos here.

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